style(chat-app): add settings back button, premium dropdown select arrows, browser mockup for preview, update free CPU models list, and refine discussion list cards

feat(chat-app): overhaul chat interface, add Claude-style sandboxed artifacts, Perplexity-style citations/sources, settings tabs, theme selector, exports, temporal grouping, and context menus

feat(chat): add dynamic download file cards, perplexity-style search logs, and timeout reliability fixes

feat: implement client-side export to ZIP, PDF, Word, and PPTX with glassmorphic dropdown UI

feat: add app favicon and startup loading overlay animation

feat: replace alerts with custom toasts

feat: add message actions toolbar

docs: add comprehensive README for chat application

feat: enhance web search logs display & fix 2023 temporal date cutoff

Correction des timeouts DNS sur reseau dual-stack (IPv6)

Ajout de l'application web/mobile standalone (cypher-chat-app), configuration de l'Espace (cypher-ai) et mise à jour vers Qwen-7B-Instruct